A tighter constraint on Earth-system sensitivity from long-term temperature and carbon-cycle observations

Area of Science:

• Paleoclimatology
• Climate modeling
• Geochemistry

Background:

• Earth system sensitivity (ESS) is crucial for understanding long-term climate responses to CO2 forcing.
• Current ESS estimates have significant uncertainties, limiting climate projections.
• Previous studies constraining ESS often used informal statistics or focused on limited paleo-data.

Purpose of the Study:

• To refine Earth system sensitivity (ESS) estimates by integrating deep-time CO2 and temperature data with a long-term carbon cycle model.
• To reduce uncertainties in ESS and improve the quantification of Earth's long-term climate response.
• To investigate the role of chemical weathering in climate dynamics over geological timescales.

Main Methods:

• Employed a Bayesian approach to fuse extensive paleo-CO2 and temperature records (last 420 million years) with a sophisticated long-term carbon cycle model.
• Utilized deep-time climate data spanning 420 million years to constrain model parameters.
• Assessed the impact of varying chemical weathering parameters, specifically reduced weatherable land area, on model-data agreement.

Main Results:

• Generated a refined median ESS estimate of 3.4 °C, with a narrower 5-95% confidence range of 2.6-4.7 °C compared to previous assessments.
• Demonstrated that reduced chemical weathering, linked to decreased weatherable land area, improves model agreement with Cretaceous temperature records.
• Identified specific mechanisms within chemical weathering as key targets for future research to further constrain ESS.

Conclusions:

• The Bayesian fusion of deep-time data and carbon cycle modeling significantly narrows ESS uncertainty.
• Chemical weathering processes, particularly those related to land area, play a critical role in long-term climate regulation and ESS.
• Further research into weathering mechanisms offers a promising pathway to enhance our fundamental understanding of Earth system properties and climate sensitivity.